1. Field of the Invention
This invention deals with serial impact printing assemblies for use in typewriters and other types of printing apparatus. In this field, the original practice was to utilize a multitude of typing bars, each having one or more of the possible characters driven sequentially into a fixed printing position. A massive platen is moved past the printing position through various mechanical means. High speed operation was inhibited by interfering flight paths of type bars and the high inertia of the movable platen due to cumbersome mechanical indexing mechanism. Printing quality was low because of the type bar flexibility and its lack of control at impact spot.
With the advent of the single element printer, the state of the art was pushed forward because it surpassed the bar type printer in speed and printing quality.
Single element printers generally fall in one of the following three types according to the arrangement of characters on the printer and thus the selection of characters during a printing cycle.
A. Disk (or daisy) type: The characters are placed on radially arranged individual cantilever arms forming a plane (and thus the name daisy) or a conical surface. Rotation accomplishes the character selection. Character imprinting is done by striking the character selected with an actuator or a ram mounted fixedly relative to the character selection motor. PA1 B. Cylindrical type: The characters are arranged in two dimensional array on the cylindrical surface of the printing element. Character selection is accomplished by rotation and lift or drop of the printing element. Printing is performed by striking the printing element on to the platen. PA1 C. Spherical type: The characters are arranged in two dimensional array on the spherical surface of the printing element. Character selection is accomplished by rotation and tilt about the center of the sphere.
As described below, when no distinction is made between the cylindrical and spherical types, "vertical" control or selecting refers to "lift" or "drop" of the former, and "tilt" of the latter. Also "drum" and "ball" will be used interchangeably with "cylindrical" and "spherical", respectively.
The present invention which applies to this more recent field of multi-character printing assemblies, utilizes a single printing element of either disk, cylindrical or spherical type.
The conventional arrangement between the single element imprinting assembly and the platen has been to move the entire imprinting assembly together with its various controls along the length of the platen during the printing of one line.
2. Description of the Prior Art
When utilizing the single printing element the prior art has always moved the single element and controls with respect to the platen rather than moving the platen with respect to the printing element.
The disk type printer has always included in the printer carrier the character selection motor, the imprinting prime mover and plunger or ram. The cylindrical and spherical printers have either employed mounting the character selection motor and imprinting motor on the printer carrier or resorted to transmitting the selection controls from stationary motors via flexible cables or metal bands. The consequence of all such arrangements is inertial interaction and dependence: i.e., an increase in power source or motor sizes for character selection and imprinting for the purpose of increasing printing speed would burden the carrier motor and decrease the overall printing speed. Auxiliary mechanisms such as ribbon movement that rode on the carrier further aggravated inertial dependence in such arrangements.
The stretching and deformation of the flexible control devices became less responsive or less reliable when higher printing speeds were attempted. Examples of the assemblies for using single element printing are shown in U.S. Pat. Nos. 2,757,775; 3,618,735; and 3,771,635. These ideas, along with many others in the prior art have been aimed at advancing the art within the confines of the existing configuration, which is plagued by inertial dependence. For the movable carrier configuration, the present state of development has reached to the point of sharp diminishing return and further increase of motor sizes has become prohibitive and unworkable.